Moving to a Target Distance

Now that you have created the constant variables needed to calculate the amount of ticks per mm moved, you can use this to set a target distance. For instance, if you would like to have the robot move forward two feet, converting from feet to millimeters and multiplying by the COUNTS_PER_MM will give you the amount of counts (or ticks) needed to reach that distance!

Create two more variables called leftTarget andrightTarget.

These variables can be fluctuated and edited in your code to tell the motors what positions to go to, rather than place them with the constant variables, create these variables within the OpMode but above the waitForStart(); command.

public void runOpMode() {
        leftmotor = hardwareMap.get(DcMotor.class, "leftmotor");
        rightmotor = hardwareMap.get(DcMotor.class, "rightmotor");
        
        rightmotor.setDirection(DcMotor.Direction.REVERSE);
        
        leftmotor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
        rightmotor.setMode(DcMotor.RunMode.STOP_AND_RESET_ENCODER);
        
        int leftTarget;
        int rightTarget;
        
        waitForStart();

The setTargetPosition();function takes in a integer (or int) data type as its parameter, rather than a double. Since both the leftTarget and rightTargetwill be used to set the target position, create both variables as int variables.

Converting from mm to Feet

Right now the main distance factor is COUNTS_PER_MM , however you may want to go a distance that is in the imperial system, such as 2 feet (or 24 inches). The target distance in this case will need to be converted to mm.

To convert from feet to millimeters use the following formula:

$$d_{(mm)} = d_{(ft)} × 304.8$$

If you convert 2 feet to millimeters, it comes out the be 609.6 millimeters. For the purpose of this guide, lets go ahead an round this to be 610 millimeters.

Converting Feet to Ticks

Next, multiply 610 millimeters by the COUNTS_PER_MM variable to get the number of ticks needed to move the robot 2 feet. Since the intent is to have the robot move in a straight line, set both the leftTarget and rightTarget, to be equal to 610 * COUNTS_PER_MM

As previously mentioned the setTargetPosition(); function requires that its parameter must be an integer data type. The leftTargetand rightTargetvariables have been set to be integers, however theCOUNTS_PER_MM variable is a double. Since these are two different data types, a conversion of data types needs to be done.

In this case the COUNTS_PER_MM needs to be converted to an integer. This is as simple as adding the line (int) in front of the double variable. However, you need to be cautious of potential rounding errors. Since COUNTS_PER_MM is part of an equation it is recommended that you convert to an integer AFTER the result of the equation is found.

int leftTarget = (int)(610 * COUNTS_PER_MM);
int rightTarget = (int)(610 * COUNTS_PER_MM);

Lastly, edit the setTargetPosition(); lines so that both motors are set to the appropriate target position. To do this add the leftTarget and rightTarget variables to their respective motor:

leftmotor.setTargetPosition(leftTarget);
rightmotor.setTargetPosition(rightTarget);